1. Field of the Invention
This invention relates to a metal corrosion inhibitor for use in aqueous solutions, and to antifreeze/coolant compositions containing such a corrosion inhibitor. More particularly, this invention relates to a corrosion inhibitor comprising a combination of alkylbenzoic and aliphatic monobasic acids and/or the alkali metal, ammonium, or amine salts of such acids, and to corrosion-inhibited aqueous and antifreeze/coolant compositions containing the same.
Automobile engine cooling systems contain a variety of metals, including copper, solder, brass, steel, cast iron, aluminium, magnesium, and their alloys. The possibility of corrosive attack on such metals is high, due to the presence of various ions as well as the high temperatures, pressures, and flow rates found in such cooling systems. The presence of corrosion products within the cooling system can interfere with heat transfer from the engine combustion chambers, which may subsequently cause engine overheating and engine component failure due to excess metal temperatures. See generally Fay, R. H., "Antifreezes and Deicing Fluids," In: Kirk-Othmer Encyclopedia of Chemical Technology (1978) ed.), vol. 3, pp. 79-95. It would therefore be generally advantageous if the formation of corrosion products within automobile cooling systems could be controlled or eliminated. It is one object of the instant invention to provide a corrosion inhibitor useful in the prevention and control of corrosion in automobile engine cooling system containing various metals.
The trend towards improved fuel economy for automobiles has led to the increased use of lightweight materials such as aluminum and magnesium alloys for engine and cooling system components. However, it has been found that pitting and crevice corrosion are particularly prevalent in aluminum-containing cooling systems. Pitting of thin-walled automobile radiator tubes may lead to tube perforation; crevice corrosion at cylinder head packings or coolant hose connections may also occur. Both types of corrosion may lead to eventual coolant loss, with subsequent engine overheating and component failure. Other forms of localized corrosion such as deposit attack from deposition of corrosion products may also result.
Many conventional corrosion inhibitor additives used in automobile cooling systems do not provide adequate protection against the pitting, crevice, and deposit attack corrosion phenomena found with aluminum and various other metal alloys. It would therefore be particularly advantageous if such localized corrosion phenomena could be controlled or eliminated. It is another object of the instant invention to provide a corrosion inhibitor for use in automobile cooling systems which prevents or controls localized corrosion of aluminum, magnesium, and various other metal surfaces.
All corrosion inhibitors employed in automobile antifreeze/coolant formulations are gradually depleted by use and the build-up of corrosion products in the cooling system. It would thus be advantageous if the build-up of corrosion products within the system and subsequent corrosion inhibitor depletion or degradation could be controlled or eliminated. It is a further object of the instant invention to provide a corrosion inhibitor which is less prone to depletion or degradation than traditional corrosion inhibitors used in antifreeze/coolant formulations.
2. Information Disclosure Statement
It is well known that various monobasic and dibasic acids as well as the salts of such acids are effected as corrosion inhibitors when employed in antifreeze/coolant formulations. For example:
U.S. patent application Ser. No. 813,902, filed on Dec. 27, 1985 (incorporated herein by reference) describes various U.S. and foreign references which disclose the use of basic acids/salts as corrosion inhibitors in antifreeze/coolant formulations, and also discloses a corrosion inhibitor which comprises the combination of a C.sub.5 -C.sub.16 aliphatic monobasic acid/salt, a C.sub.5 -C.sub.16 hydrocarbyl dibasic acid/salt, and a hydrocarbyl triazole for use in engine antifreeze/coolant systems;
U.S. patent application Ser. No. 819,321, filed on Jan. 16, 1986 discloses a stabilized corrosion-inhibited antifreeze/coolant formulation which comprises at least one C.sub.5 -C.sub.16 monobasic or dibasic acid/salt and a precipitation-inhibiting hydrocarbyl aminophosphonic acid/salt or polyacrylic acid/polyacrylate stabilizer; and
U.S. patent application Ser. No. 847,076, filed Apr. 1, 1986 discloses a corrosion-inhibited antifreeze composition comprising a C.sub.5 -C.sub.16 aliphatic monobasic acid/salt, a C.sub.5 -C.sub.16 hydrocarbyl dibasic acid/salt, a hydrocarbyl azole, and a hydrocarbyl C.sub.10 -C.sub.20 alkali metal sulfonate.
The general use of alkylbenzoic acids/salts as corrosion inhibitors is also well known. For example, U.S. Pat. Nos. 4,501,667, 4,402,907, and 4,366,076 disclose that alkylbenzoic acids such as 4-tert-butylbenzoic acid are useful as metal corrosion inhibitors. In addition:
U.S. Pat. No. 4,552,678 discloses a corrosion inhibitor obtained from the reaction product of a polyamine, an anhydride, and an organic acid of the formula R.sub.2 --COOH where R.sub.2 may be H, a C.sub.1 -C.sub.12 alkyl C.sub.1 -C.sub.5 hydroxyalkyl, phenyl, tert-butyl, phenyl, or styryl radical; PA1 U.S. Pat. No. 3,769,214 discloses an aqueous lubricant composition containing a minor amount of a metal anti-staining agent and stability improver which is an alkanolamine salt of a carboxylic acid having at least 12 carbon atoms per molecule; PA1 U.S. Pat. No. 2,832,742 discloses the use of a blend of the diethanol amine salts of p-tert-butylbenzoic acid and a high molecular weight C.sub.7 -C.sub.18 aliphatic carboxylic acid mixture derived from an oxidized petroleum fraction; PA1 Japanese Pat. No. 59208082 discloses a method of inhibiting corrosion in a cooling water system for an internal combustion engine via addition of a corrosion inhibitor containing a water soluble amine salt of benzotriazole, a water soluble amine salt of t-butylbenzoic acid, a nitrite, and a benzoate to the cooling water; and PA1 API Primary Petroleum Products Abstract No. 76-20709 describes French Pat. No. 2268791, which discloses a water soluble ferrous metal corrosion inhibitor which is the condensation product of a C.sub.1 -C.sub.6 para-alkylbenzoic acid and an alkanolamine. PA1 (a) an alkylbenzoic acid or the alkali metal, ammonium, or amine salt thereof, said acid having the general formula ##STR2## where R is a C.sub.1 -C.sub.5 alkyl radical; (b) a C.sub.8 -C.sub.12 aliphatic monobasic acid or the alkali metal, ammonium, or amine salt thereof; and PA1 (c) a hydrocarbyl triazole.